Atlanta real estate company Portman Holdings LLC will develop a $300 million mixed-use project and high-performance computing center for Georgia Tech in Midtown’s Technology Square. Georgia Tech said it got the OK to proceed with the project at today’s meeting of the Board of Regents of the University System of Georgia. Tech confirmed it chose Portman Holdings as the project developer. The mixed-use development would rise over Tech Square on the site that housed the Crum & Forster building at 4th and Spring streets.